I have an '84 FBody with carbureted 2.8L and 700R4. I have finally gotten to a point where I'll be replacing the carb/distributor with components from an S10 which means I'll be losing the TPS input to the ECM and subsequently it will not be controlling the TCC lock-up.

I've researched a number of threads here going back many years and came up with a potentially simple approach to dealing with this common issue. While I don't have a problem with spending a little extra $ on a 'kit' - it seems they are (understandably) as much about retrofitting 700R4s to earlier cars as about dealing with losing ECMs control in newer cars (such as 3rd gens) which already have most of the 'stuff' on them for controlling 700R4s.

I'm not going for performance here - but rather functionality, economy and longevity.

There is a suggestion to wiring a switch into the F port on the ALCL. I was already familiar with the 'F' port on the ALCL from when I had to debut my TCC (was the brake switch) some years ago.

So here is yet another possible solution:

Why not simply install an NO vacuum switch such as the #71V or #71V2 to the F connector on the ALCL and then ground the vacuum switch and run a vacuum line to it?That's it!

(Universal adjustable vacuum switch)

The vacuum switch could be installed on the firewall, grounded to the body and a wire run under the dash and spliced to the wire leading to the 'F' connector on the ALCL. A vacuum hose run to probably the same source as the (yet to be installed) vacuum advance source with a plastic 'T'.

This would allow all the stock wiring to stay in place and require a minimal amount of effort and cost. Even without a functional ECM - I believe this should work.

Lockup would occur in high vacuum conditions when the switch closes (grounding 'F') and and it would unlock in low vacuum conditions when the switch opens (ungrounding 'F').

Same as the various kits - this would lockup even when cold - the factory setup keeps the TCC unlocked when cold to help with faster warm-up of drivetrain. No biggee - I think that function will be lost regardless of approach.

Question:
Will this work? Or did I miss some gotcha?
Question:
What advantages does a kit such as TCI P/N 376600 $79.88 have over a simple vacuum switch grounding the 'F' connector on the ALCL?

I'm thinking the kits just lockup 4th. This approach would lockup 2nd thru 4th under low throttle. Remember I'm not going for performance with a 2.8L. But I'm not sure how this would affect driveability.

Again - I don't have a problem spending extra for a kit if there's some functionality or other design aspects worth considering.

OK I slept on it and realized at least two disadvantages to putting a simple vacuum switch off the 'F' connector:

1) It will not disengage lockup in 4th when coasting - thus engine braking like with a manual transmission.

2) 2nd and 3rd will also be locked under light or maybe medium acceleration. That might be hard on the transmission over time? Also it might be a bit noticeable in overall performance with a low powered V6.

Sooooo I think I'll stick with one of the popular 'kits' as outlined in the link above.

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There are two basic 'types' of kits as to installation/components:

1) Internal kits - internal components like the TCC solenoid are replaced after dropping the pan...

2) External kits - purely works with external connectors/sensors on the 700R4.

Costs seem comparable. I don't mind dropping the pan - I drop it every couple/few years anyway to change fluid/filter.

QUESTION: In the end which approach is better? What are the trade-offs between the internal vs external kit approaches to locking 700R4's TCC in 4th gear?

I got the TCI kit and it is a very easy install, especially if you are planning to change fluids anyway. Just dont use the pan gasket they give you...it blows. The vaccum switch in the kit is adjustable to a certain degree to make sure that you can get the lock up right. I dont have the experience with the external kits but if your going the full carb route and all having the TCI switch I think would just be easier in the end. Less electronics and reliance on any of the older GM parts already on the car/ tranny.

I think im going to just run a switch because i can't afford the kits as of right now & i really don't wanna drop the pan and start messing with stuff. Also don't wanna put any unnessiscary damage on my trans. running it in OD without the converter being locked up.